The long range version of the Inceptors (and at that matter the only Primaris unit with a 48" range weapon), Suppressors function as a complement to your Reivers and Assault Squads, with a special rule on their autocannons taking away an enemy's ability to fire overwatch if they get a kill, making them great at helping your Reivers clear our hordes and gunlines. The Sergeant also has a smoke launcher, which he can use once per game to make all enemy units take a -1 to hit on the unit until your next shooting phase, making them excellent at last stands (Sergeant uses smoke launcher, squad shoots autocannons into unit to take away overwatch, unit gets -1 to hit their fight phase, and, even if they fall back, any units shooting them still get the negative modifier).

That said, apart from being AP-2 the autocannons are no stronger than any other Imperial autocannon, so anything with heavy armor, high Toughness or lots of wounds will require support from other units, like Hellblasters or Devastators with Lascannons.